1. Field of the Invention
This invention relates to measuring opto-electrochemical properties of a fluid or fluid mixture, or other properties of the fluid or fluid mixture based on the opto-electrochemical properties, using a simple integrated sensing cell. The system would be used to measure or calculate the properties of industrial fluids or fluid mixtures, and provide the necessary information to properly control the operation and treatment of an industrial fluid system.
2. Description of Related Art
Accurate measurement of various properties in industrial fluid systems, such as cooling towers and boiler systems, is required to assure proper performance, safety, and reliability of the fluid system, and to reduce unit lifetime costs of components in the fluid system. There are numerous sensing methods used to measure process fluids, but two of the more common are optical and electrochemical. Typically, measurement of an optical property, such as fluorescence, absorbance, or transmission, and measurement of an electrochemical property, such as conductivity, involves the use of two separate measurement instruments and two separate samples from the fluid system. For example, a fluorometer and a conductivity meter may be used in series, as described in U.S. Pat. No. 4,112,741, to measure optical and electrochemical properties in a body of water. As additional examples, U.S. Pat. Nos. 4,783,314 and 6,369,894 disclose the fluorometric measurement of the concentration of a fluorescent tracer included in a treatment product added to an industrial fluid system, which is indicative of the concentration of the treatment product in the fluid system, in conjunction with a separate conductivity meter used in the fluid system. The results of these measurements may then be used to adjust various operating parameters within the fluid system in order to control the fluid system. Other methods and devices are known for using data from various measured properties to control a fluid system. For example, U.S. Pat. No. 6,280,635 discloses the use of fluorescence and make-up water composition to control a cooling tower. A complex matrix control platform is disclosed in U.S. Pat. No. 6,315,909, where separately measured conductivity and fluorescence are two tools that may be used to make adjustments to the fluid system.
It is also known to conduct fluorometric and conductivity measurements on the same sample of water, but using a fluorometer and a separate conductivity meter that are not integrated into a single, hand-held device. For example, U.S. Pat. No. 5,691,809 discloses a system to monitor fluid phase changes in processing of crude oil and other organic liquids. The system in the '809 patent uses a heated, pressurized cell containing a sample of the liquid to be analyzed in contact with electrodes. The cell is connected to a fiber optic probe and fluorometer external to the cell and to an external conductivity meter. Additionally, the conductance is measure by a disk electrode and the pressure cell body. This configuration is known to lack sensitivity as demonstrated in FIG. 5 of the '809 patent, where the range of change is small, and would be insufficient for monitoring most industrial process fluids.
More complex instruments that combine fluorometric and conductivity or other electrochemical property measurements into a single device are also known. For example, dip-type or immersion-type sensors are disclosed in U.S. Pat. Nos. 7,550,746 and 8,440,062 for measuring fluorescence and conductivity. These instruments are immersed into the water being tested, which may result in inaccurate measurements. The complexity of the multi-component sensor system in the '062 patent also requires the conductance electrodes to be floated while taking measurements with the other electrochemical electrodes, creating a risk of inaccurate bridge balance when making a conductance measurement. A flow-through sample cell instrument for measuring fluorescence, absorption, and conductivity is disclosed in U.S. Pat. No. 4,555,936. The electrodes act as inlet and outlet flow conduits for the sample to pass through the sample cell. Measuring conductivity with flowing fluid, and where mixing in a square cell configuration, would be prone to errors.
Measuring conductivity and fluorescence in blood samples is also disclosed in U.S. Pat. No. 6,228,652. The instrument disclosed in the '652 patent uses a standard configuration for fluorescence measurements, but with a multitude of filters, mirrors, and photomultiplier tubes. The conductance measurement uses two electrodes, but it measures radio frequency (RF) Conductance where the conductivity is proportional to the dissipation of the RF power. This was designed to measure the conductance inside the blood cell, and it requires that the field be focused at the small cell window where the single cell is being measured. Additionally, the sample cell is a cytometric flow-through cell designed to allow blood cells to pass through one at a time. The measurement approach disclosed in the '652 patent would be inappropriate for a bulk fluid or fluid mixtures.
Several prior art instruments utilize multiple photodetectors and a single light source to measure multiple optical properties or improve upon fluorescence detection. For example, the '936 patent measures fluorescence and absorbance and U.S. Pat. No. 7,652,267 measures fluorescence and turbidity. A second photodetector in the '267 and '894 patents may also be used as a reference detector to measure UV intensity to provide correction of the fluorescent signal. Additional photodetectors are also disclosed in the '652 patent to correspond to the number of fluorescence spectra emitted by the dyes and fluorochromes in the sample. Two light sources are also disclosed in U.S. Pat. No. 7,095,500, one being an excitation light source and a second light source that does not induce fluorescence, but is used to correct for effects on the fluorescent measurement due to fouling or turbidity. To provide measurements of additional optical properties, multiple instruments may be stacked together in a modular device or have interchangeable parts. For example, the '894 patent discloses stacking between two and sixteen modular flourometers, each having a flow-through sample cell, a light source, and two photodetectors to measure fluorescence of different species when the water sample contains multiple species with different emission spectra. The '500 patent discloses an interchangeable probe tip with each tip having a different optical configuration to measure different properties, such as fluorescence and absorbance, so that the tips have to be changed out between measurements to measure both properties.
None of the known references disclose a single unit having multiple light sources and multiple optical detectors to measure multiple properties on a single sample contained within a sample cell. Additionally none of the known references disclose combining optical property detection with detection of multiple electrochemical properties, through the use of two or more electrodes, in a single device. Nor do any of the known references disclose comparing the results of an optical measurement with an electrochemical measurement obtained by a single device to enhance the control of a fluid system. There is a need for a simple, integrated, hand-held system that is capable of accurately measuring and calculating multiple properties of a fluid sample based on optical and electrochemical data or signals from a single sample. There is also a need for a system and method that can improve the operation of a fluid system by using data from at least one optical property-based measurement and at least one electrochemical property-based measurement to control operating parameters of the fluid system.